Enhancement of terbium efficiency by gallium and copper co-doping in(Pr,Nd)-Fe-B sintered magnets

It is well known that Tb substitution for(Pr,Nd)in(Pr,Nd)-Fe-B based sintered magnetic materials is an effective way to increase intrinsic coercivity,but it is not quite clear whether the increment depends on the different matrix phases with various doping ingredient or not,which is essential to develop high quality magnets with high coercivity more efficiently and effectively with economic consumption of expensive Tb and other costly heavy rare earths.In this paper,we investigated the efficiency of Tb substitution for magnetic property in(Pr,Nd)-Fe-B sintered permanent magnets by co-doping Ga and Cu elements.It is shown that Ga and Cu co-doping can effectively improve the efficiency of Tb substitution to increase the thermal stability and the coercivity.The intrinsic coercivity increases up to 549 and 987 kA/m respectively by 1.5 wt%and 3.0 wt%Tb substitution in Ga and Cu co-doped magnets while the intrinsic coercivity increases up to only 334 and 613 kA/m respectively by the same amounts of Tb substitution in non-Ga and low-Cu magnets.In other words,it demonstrates that there is about 329-366 kA/m linear equivalent enhancement of intrinsic coercivity by 1.0 wt%Tb substitution for(Pr,Nd)in Ga and Cu co-doped magnets.The temperature coefficients of both intrinsic coercivityβand remanenceαat 20-150℃by 3.0 wt%Tb substitution for the magnets with Ga and Cu co-doping are-0.47%/K and-0.109%/K respectively,and in contrast those values are-0.52%/K and 0.116%/K respectively for the non-Ga and low-Cu magnets.It is the principal reason for more efficient enhancement of magnetic property by Tb substitution in the Ga and Cu co-doped magnets in which Tb atoms are expelled from triple junction phases(TJPs)to penetrate into the grain boundary phases(GB phases)and thus modify the grain boundary.It is prospected that the efficiency of Tb substitution would rely on different matrix phases with various doping constituents.

Effect of aluminum on microstructure and magnetic properties of sintered Nd-Fe-B magnets processed by grain boundary diffusion of Tb-Al

The grain boundary diffusion process(GBDP)of Tb can improve the coercivity of sintered Nd-Fe-B magnets.In this study,the effect of AI on the diffusion of Tb in the GBDP was investigated.The content of diffused Tb-Al was precisely controlled by adjusting the magnetron sputtering process.The Tb equivalent of Al was also studied.Results show that AI promotes the diffusion of Tb deeper into the magnet,reducing the thickness of the shell in the core-shell structure.This study is helpful for further developing the process,reducing the consumption of heavy rare earth elements(Tb),and improving the coercivity of sintered Nd-Fe-B magnets.

Extraordinary simultaneous enhancement of the coercivity and remanence of dual alloy HRE-free Nd-Fe-B sintered magnets by post-sinter annealing

Post-sinter annealing process plays an important role in the microstructures and magnetic properties of the Nd-Fe-B sintered magnets.In this paper,systematically investigated are the magnetic properties and microstructures of the as-sintered and post-sinter annealed Nd-Fe-B magnets with Pr-Fe-Ga boundary addition.Two choice consecutive annealing methods are adopted at high and low temperatures,namely the 1 st annealing at 880℃ for 2 h and then the 2^(nd) annealing at 440℃ for 3 h.It is exceptional to find out that both the remanence and coercivity are improved after 2^(nd) annealing process for this type of magnet.The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2^(nd) annealed magnet,with a significant increment of 70.37%in coercivity.The extraordinary magnetic properties of B_(r)=14.44 kGs,H_(cj)=17.19 kOe and(BH)_(max)=51.08 MGOe are obtained for the designated Nd-Fe-B sintered magnets without heavy rare earth(HRE)elements manufactured by dual alloy method.The Curie temperature is monotonically decreased from 634 K to 602 K while the c-axis alignment degree is optimized after annealing.Microstructural observation and analysis indicate that the elemental distribution patterns are altered after the 2^(nd) annealing.The diffusion of the aggregate(Pr,Nd,Cu,Ga)-rich phase from triple junctions into the grain boundary regions is ascribed to the formation of thin and continuous grain boundary layer,which is critical to improve the microstructures and magnetic properties.

Enhanced magnetic properties and improved corrosion performance of nanocrystalline Pr-Nd-Y-Fe-B spark plasma sintered magnets

Recently it is a hot topic to make full use of high abundant Y element in Nd_(2)Fe_(14)B-type permanent magnets.In contrast to Pr and Nd elements,Y shows different metallurgical behaviors during preparation process.In this paper,we have explored the magnetic properties,microstructures and corrosion performance of Pr-Nd-Y-Fe-B magnets fabricated by spark plasma sintering(SPS)technique from the ribbons of nanocrystalline and amorphous precursors,respectively.The coercivity and maximum energy product were improved for the magnets prepared from amorphous precursor materials(denoted as SPS-A hereafter)compared with the magnets prepared from crystalline precursor materials(denoted as SPS-C hereafter).Magnetic properties of Jr=0.79 T,Hci=864 k A/m,and(BH)_(max)=102 k J/m^(3)were obtained for SPS-A magnets.In contrast with SPS-C magnets,the magnetic properties of SPS-A magnets are not so sensitive to the preparation conditions,which is quite beneficial to the homogeneity of microstructure and enhancement of coercivity for large-scale production of the designated magnets.Aggregated(Pr,Nd,Y)-rich phase was found out in SPS-C magnets.Pr and Nd elements are rich at grain boundary while Y is distributed uniformly at main phase and grain boundary phase.The strip grains and equiaxed grains exist in SPS-C and SPS-A magnets,respectively.The enhanced magnetic properties for SPS-A magnets are accredited to the uniform distribution of rare-earth-rich phase and low demagnetization factor.It is revealed by electrochemical test and dipping test that the corrosion potential is more positive and the corrosion rate is slower for the SPS-A magnets in 3.5 wt.%Na Cl solution.The work is also expected to shed light on developing the nanocrystalline Pr-Nd-Y-Fe-B SPSed high-performance magnets in industry.